NIO中，java.nio.charset.MalformedInputException

<!-- [if gte mso 9]><xml> <w:WordDocument> <w:View>Normal</w:View> <w:Zoom>0</w:Zoom> <w:PunctuationKerning/> <w:DrawingGridVerticalSpacing>7.8 磅</w:DrawingGridVerticalSpacing> <w:DisplayHorizontalDrawingGridEvery>0</w:DisplayHorizontalDrawingGridEvery> <w:DisplayVerticalDrawingGridEvery>2</w:DisplayVerticalDrawingGridEvery> <w:ValidateAgainstSchemas/> <w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid> <w:IgnoreMixedContent>false</w:IgnoreMixedContent> <w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText> <w:Compatibility> <w:SpaceForUL/> <w:BalanceSingleByteDoubleByteWidth/> <w:DoNotLeaveBackslashAlone/> <w:ULTrailSpace/> <w:DoNotExpandShiftReturn/> <w:AdjustLineHeightInTable/> <w:BreakWrappedTables/> <w:SnapToGridInCell/> <w:WrapTextWithPunct/> <w:UseAsianBreakRules/> <w:DontGrowAutofit/> <w:UseFELayout/> </w:Compatibility> <w:BrowserLevel>MicrosoftInternetExplorer4</w:BrowserLevel> </w:WordDocument> </xml><![endif]--><!-- [if gte mso 9]><xml> <w:LatentStyles DefLockedState="false" LatentStyleCount="156"> </w:LatentStyles> </xml><![endif]--> <!-- [if gte mso 10]> <mce:style><!-- /* Style Definitions */ table.MsoNormalTable {mso-style-name:普通表格; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;} --> <!-- [endif]-->

从一段错误的代码中联系到的

最近刚开始学习 NIO ，网上搜了一个 IBM 的 NIO 学习资料，感觉学习难度不大，因为我自认为自己之前 IO 基础学得还不错。没想到我使用 NIO 编写的第一个程序，就让我感悟颇深。

下面请大家看看我写的这个类：

package com.hepeng.test;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.channels.FileChannel;
import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
public class ReadFile0 {
	public static void main(String[] args) {
		FileInputStream fis = null;
		FileChannel fc = null;
		try {
			//1.从FileInputStream获取通道
			fis = new FileInputStream("E://NIO//NioTcpServer.java");
			fc = fis.getChannel();
			//2.创建Buffer
			ByteBuffer byteBuffer = ByteBuffer.allocate(100);
			
			Charset gb2312 = Charset.forName("GB2312");
			CharsetDecoder decoder = gb2312.newDecoder();
			
			//3.把通道中的数据读到byteBuffer中。
			while (true) {
				byteBuffer.clear();
				if (fc.read(byteBuffer) == -1)
					break;
				
				byteBuffer.flip();
				CharBuffer charBuffer = decoder.decode(byteBuffer);
				
				charBuffer.flip();
				while (charBuffer.hasRemaining())
					System.out.print(charBuffer.get());
			}
		}
		catch (FileNotFoundException e) {
			e.printStackTrace();
		}
		catch (IOException e) {
			e.printStackTrace();
		}
		finally {
			try {
				if (fc != null) {
					fc.close();
				}
				if (fis != null) {
					fis.close();
				}
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
	}
}

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感觉没什么毛病，自我感觉很良好嘛， ^_^ 很多时候，当我们自己感觉良好的时候，往往事实上是很不良好。

一运行，出现了红得刺眼的异常信息， -_-! ：

java.nio.charset.MalformedInputException: Input length = 1
	at java.nio.charset.CoderResult.throwException(CoderResult.java:260)
	at java.nio.charset.CharsetDecoder.decode(CharsetDecoder.java:781)
	at com.hepeng.test.ReadFile0.main(ReadFile0.java:33)

<!-- [if gte mso 9]><xml> <w:WordDocument> <w:View>Normal</w:View> <w:Zoom>0</w:Zoom> <w:PunctuationKerning/> <w:DrawingGridVerticalSpacing>7.8 磅</w:DrawingGridVerticalSpacing> <w:DisplayHorizontalDrawingGridEvery>0</w:DisplayHorizontalDrawingGridEvery> <w:DisplayVerticalDrawingGridEvery>2</w:DisplayVerticalDrawingGridEvery> <w:ValidateAgainstSchemas/> <w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid> <w:IgnoreMixedContent>false</w:IgnoreMixedContent> <w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText> <w:Compatibility> <w:SpaceForUL/> <w:BalanceSingleByteDoubleByteWidth/> <w:DoNotLeaveBackslashAlone/> <w:ULTrailSpace/> <w:DoNotExpandShiftReturn/> <w:AdjustLineHeightInTable/> <w:BreakWrappedTables/> <w:SnapToGridInCell/> <w:WrapTextWithPunct/> <w:UseAsianBreakRules/> <w:DontGrowAutofit/> <w:UseFELayout/> </w:Compatibility> <w:BrowserLevel>MicrosoftInternetExplorer4</w:BrowserLevel> </w:WordDocument> </xml><![endif]--><!-- [if gte mso 9]><xml> <w:LatentStyles DefLockedState="false" LatentStyleCount="156"> </w:LatentStyles> </xml><![endif]--> <!-- [if gte mso 10]> <mce:style><!-- /* Style Definitions */ table.MsoNormalTable {mso-style-name:普通表格; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;} --> <!-- [endif]-->

仔细一分析，发现：

拿到一个字节的 buffer 后，我竟然随意的对其进行 decode ，哎，只能骂自己头脑简单——怎么能随随便便就对一个 ByteBuffer 进行字符的解码呢？原因是： java 中一个汉字是由 2 个字节组成，但是谁能保证我这 buffer 里面都可以成功解码成汉字呢？其中也许有“半个汉字”也说不准哦。于是 decoder 说“半个汉字，你让我怎么解码！！！”（第 33 行的异常 ）

通常的解决思路是：每次都去判断一下：Bytebuffer中最后一个字节是否合法；如果不合法，则说明这个字节是双字节汉字的一部分，这样我们解码时就不要包含这个字节，而是把这个字节放进下次解码之前的Bytebuffer中。这样做，系统就不会抛出“无法正确解码”这类的异常了。

现在来看， NIO 真的适合用来显示文件内容？答案是：不适合。其实 NIO 主要是使用在 socket 网络编程领域，它的出现也仅仅为了弥补 IO 在网络编程中的缺憾。不错， NIO 并不是为了取代 IO 而登上历史舞台的。